The present invention generally relates to a semiconductor device production method and a semiconductor device, and more particularly to a production method of a semiconductor device in which an adjustable circuit, having a circuit element with electric properties adjustable through a laser trimming, is formed on a semiconductor chip, and to the semiconductor device produced by the method of production.
As disclosed in Japanese Laid-Open Utility Model Application No.6-13148, there is known a semiconductor device in which a semiconductor chip is packaged or molded with a transparent material. FIG. 3 shows such a semiconductor device that is disclosed in the above-mentioned publication.
In the semiconductor device of FIG. 3, an IC (integrated circuit) chip is packaged or molded with a transparent plastic material. The wafer chip within the semiconductor device is visible from a corresponding portion 1A for the transparent plastic material, and only the portion 1A can penetrate a UV (ultraviolet) light. The remaining portions 5A of the upper surface of the semiconductor device are coated, printed or vacuum-deposited with an opaque material so that the remaining portions are opaque to external light.
In the semiconductor device disclosed in the above publication, the IC chip packaged with the transparent plastic material is an EPROM (erasable programmable read-only memory) in which data of the integrated circuit (IC) on the semiconductor device is erasable by irradiating UV light externally to the IC through the transparent plastic portion.
Further, as disclosed in Japanese Laid-Open Patent Application No.5-94905, there is known a production method that produces a semiconductor device including an adjustable resistor formed on a semiconductor chip, the adjustable resistor having electric resistance adjustable through a laser trimming. FIG. 4 shows such a production method that is disclosed in the above-mentioned publication.
As shown in FIG. 4, in the conventional production method, a semiconductor device 2B on a substrate 1B is coated with an opaque resin 5B, and a resistor 3B is separately formed on the substrate 1B. After the coating is performed, a laser beam 6B is irradiated to the resistor 3B to cut part of the resistor 3B so that the electric resistance of the resistor 3B is adjusted through the laser trimming. It is possible for the conventional production method to adjust the resistance of the resistor 3B without altering the adjustment resistance values of the semiconductor device 2B that are already finalized.
In the conventional production method of FIG. 4, a tester 7B is used to observe the resistance values of the semiconductor device 2B before and after the laser trimming is performed. The opaque resin 5B which fully covers the semiconductor device 2B serves to inhibit the laser beam 6B from influencing the resistance values of the semiconductor device 2B.
In the IC chip requiring the laser trimming (or the semiconductor device of the above type), the adjustable circuit including a circuit element, such as a fuse or a wiring, is formed on the semiconductor chip, and the electric properties of the circuit element, such as voltage, current or frequency values, are adjustable through the laser trimming. Herein, the laser trimming means that the whole or a part of the circuit element be cut away by irradiation of a laser beam. However, it is possible to extend the meaning of the laser trimming to include connection or welding operations to establish a connection of the wiring by irradiation of a laser beam.
In the above-described semiconductor device, the laser trimming is normally performed with the semiconductor chip in the wafer condition, and thereafter the assembly process is performed so that the semiconductor device is packaged.
More specifically, when the delivery of the products or samples of the semiconductor device of the above type to the customer is needed, it is necessary to perform the laser trimming with the semiconductor chip in the wafer condition, so that the electric properties of the adjustable circuit element in the semiconductor device, such as voltage, current or frequency values, are adjusted by the laser trimming so as to be in conformity with the customer""s demanded values. Hereinafter, the needed laser trimming operation is called the user customizing operation.
When performing the user customizing operation, the laser trimming is performed with the semiconductor chip in the wafer condition to meet the customer demands, and thereafter the assembly process is performed so that the semiconductor chip is packaged. Finally, the final test is conducted, and the products or samples of the semiconductor device, passing the final test, are delivered to the customer.
In the assembly process, the semiconductor chip is cut off from the wafer, and the semiconductor chip is mounted on the tab. After the mounting is performed, the wire bonding is performed between the semiconductor chip, mounted on the tab, and the lead frame. After the wire bonding is performed, the semiconductor chip, connected to the lead frame by the wires, is packaged with the resin or molding material. Hereinafter, the assembly process will be considered as the assembly process including these steps.
In the final test, it is determined whether the semiconductor chip that is packaged with the resin material at the end of the assembly process meets the customer demands. Then, the products or samples of the semiconductor device passing the final test are delivered to the customer.
However, in the semiconductor device of FIG. 3, the data of the integrated circuit on the EP-ROM is erasable by irradiating UV light externally to the IC through the transparent plastic portion 1A. Hence, the UV light used in the semiconductor device of FIG. 3 is quite different from the laser beam used in the semiconductor device in which the adjustable circuit having the circuit element with electric properties adjustable through the laser trimming is formed on the semiconductor chip.
Further, in the semiconductor device production method of FIG. 4, the opaque resin 5B which fully covers the semiconductor device 2B serves to inhibit the laser beam 6B from influencing the resistance values of the semiconductor device 2B. It is impossible to adjust the resistance values of the semiconductor device 2B by irradiating the laser beam to the semiconductor device 2B through the opaque resin 5B. There is a problem in that it is difficult for the production method of FIG. 4 to perform the laser trimming for adjusting the electric properties of the circuit elements in the semiconductor device 2B that is fully covered with the opaque resin 5B.
As described above, in a conventional production method, when performing the user customizing operation, the laser trimming is performed with the semiconductor chip in the wafer condition to meet the customer demands, the assembly process is subsequently performed so that the semiconductor chip is packaged, and finally, the final test is conducted so that the products or samples of the semiconductor device, passing the final test, are delivered to the customer. Normally, when the conventional production method is used, it takes one through three months from the receiving of the customer""s order to the delivery of the products or samples to the customer. The above conventional production method is difficult to provide speedy delivery of the products or samples to the customer in response to the customer""s order. Further, it is difficult to obtain the customer satisfaction with the conventional production method.
A conceivable method for shortening the period from the receiving of the customer""s order to the delivery of the products or samples to the customer is to always prepare a large stock for each of the samples of the semiconductor device that are expected to respectively meet various kinds of the customer demands. However, the cost for the preparation of the large stock is significantly increased. In addition, the conventional production method which requires the repetitive user customizing operation, including the laser trimming, the assembly process and the final test, each time the customer""s order is received, is not efficient in increasing the productivity.
In the above-described user customizing operation, the packaging of the semiconductor chip with the resin material is performed after the laser trimming is performed. The electric properties of the circuit element adjusted by the laser trimming may be considerably influenced by the stress or heat produced during the packaging process. If the electric properties of the circuit element are changed by the stress or heat during the packaging process, it is very difficult to restore the electric properties of the circuit element adjusted by the laser trimming.
In order to overcome the problems described above, preferred embodiments of the present invention provide an improved semiconductor device production method which reduces the amount of stock needed for each of the samples of the semiconductor device that are expected to respectively meet various kinds of the customer demands, and shortens the period from the receiving of the customer""s order to the delivery of the products or samples to the customer in order to allow speedy delivery of the products or samples to the customer in response to the customer""s order.
Another object of the present invention is to provide an improved semiconductor device which reduces the amount of stock needed for each of the samples of the semiconductor device that are expected to respectively meet various kinds of the customer demands, and shortens the period from the receiving of the customer""s order to the delivery of the products or samples to the customer in order to allow speedy delivery of the products or samples to the customer in response to the customer""s order.
Another object of the present invention is to provide a semiconductor device production method and a semiconductor device which eliminates the need to always prepare a large stock for each of the samples of the semiconductor device that are expected to respectively meet various kinds of the customer demands, so that the amount of the stock is effectively reduced.
Another object of the present invention is to provide a semiconductor device production method and a semiconductor device which can restore the electric properties of the circuit element of the adjustable circuit to the initial level by a subsequent laser trimming even when the electric properties of the circuit element adjusted by the initially performed laser trimming are changed by the stress or heat during an extended period of time.
The above-mentioned objects of the present invention are achieved by a semiconductor device production method for producing a semiconductor device in which an adjustable circuit is formed on a semiconductor chip, the adjustable circuit having a circuit element with electric properties that are adjustable through a laser trimming, the production method including the steps of: packaging the semiconductor chip with a transparent material which penetrates a laser beam within a predetermined range of wavelength having sufficient energy to cut part of the adjustable circuit; and trimming part of the adjustable circuit to obtain a target value for the adjustable circuit by focusing, after the packaging step, the laser beam onto the adjustable circuit from an upper surface of the semiconductor chip through the transparent material.
According to the semiconductor device production method of the above preferred embodiment, the assembly process is performed, in advance, for the semiconductor device to which the laser trimming is not entirely or partially performed, and a small stock of products or samples of the semiconductor device is prepared. At the time of receiving of the customer""s order, the user customizing operation is performed for the stock of the products or samples of the semiconductor device so that the laser trimming is performed to meet the customer demands. The assembly process of the user customizing operation required by the conventional production method is no longer needed. After the laser trimming is performed, the final test is conducted so that the products or samples of the semiconductor device, passing the final test, are delivered to the customer. Therefore, the semiconductor device production method of the above preferred embodiment is effective in reducing the amount of stock needed and in shortening the period from the receiving of the customer""s order to the delivery of the products or samples to the customer. It is possible for the semiconductor device production method of the above preferred embodiment to provide speedy delivery of the products or samples to the customer in response to the customer""s order and to easily obtain the customer satisfaction.
As the speedy delivery of the products or samples to the customer is possible, the semiconductor device production method of the above preferred embodiment is effective in eliminating the need to always prepare a large stock for each of the samples of the semiconductor device that are expected to respectively meet various kinds of the customer demands, and effective in increasing the productivity.
According to the semiconductor device production method of the above preferred embodiment, even when the electric properties of the circuit element of the adjustable circuit adjusted by an initially performed laser trimming are changed by the stress or heat during an extended period of time, the electric properties of the circuit element can be restored to the initial level by a subsequent laser trimming.
Further, the above-mentioned objects of the present invention are achieved by a semiconductor device which includes a semiconductor chip and an adjustable circuit provided on the semiconductor chip, the adjustable circuit having a circuit element with electric properties that are adjustable through a laser trimming, wherein the semiconductor chip is packaged with a transparent material which penetrates a laser beam within a predetermined range of wavelength having sufficient energy to cut part of the adjustable circuit, and the semiconductor device is configured such that part of the adjustable circuit is cut to obtain a target value for the circuit element of the adjustable circuit by focusing, after the packaging of the semiconductor chip, the laser beam onto the adjustable circuit from an upper surface of the semiconductor chip through the transparent material.
According to the semiconductor device of the above preferred embodiment, the assembly process, including the packaging process, is performed, in advance, for the semiconductor chip to which the laser trimming is not entirely or partially performed, and a small stock of samples of the semiconductor device is prepared. At the time of receiving of the customer""s order, the user customizing operation is performed for the semiconductor device so that the laser trimming is performed to meet the customer demands. After the laser trimming is performed, the final test is conducted so that the products or samples of the semiconductor device, passing the final test, are delivered to the customer. Therefore, the semiconductor device of the above preferred embodiment is effective in reducing the amount of stock needed and in shortening the period from the receiving of the customer""s order to the delivery of the products or samples to the customer. It is possible for the semiconductor device of the above preferred embodiment to allow speedy delivery of the products or samples to the customer in response to the customer""s order and to obtain the customer satisfaction.